Reduce noisy Gemini batch failure warnings

backend/services/ranker.go

@@ -105,7 +105,7 @@ func EvaluateAllCandidatesWithGemini(service *GeminiService, query string, ranke
 }
 
 func EvaluateAllCandidatesWithGeminiWithDeadline(service *GeminiService, query string, ranked []SearchResult, deadline time.Time) ([]AIRecommendation, GeminiBatchStats, error) {
-	const chunkSize = 8
+	const chunkSize = 6
 	const maxConcurrentBatches = 2
 	if service == nil {
 		return nil, GeminiBatchStats{}, fmt.Errorf("gemini service is not configured")
@@ -187,6 +187,7 @@ func EvaluateAllCandidatesWithGeminiWithDeadline(service *GeminiService, query s
 				})
 			}
 			recovered, recoveredErrs := recoverGeminiBatchSequentially(service, query, ranked, batch.index*chunkSize)
+			hardErrs := filterHardGeminiErrors(recoveredErrs)
 			if len(recovered) > 0 {
 				stats.SequentialRetried++
 				stats.Succeeded++
@@ -197,9 +198,9 @@ func EvaluateAllCandidatesWithGeminiWithDeadline(service *GeminiService, query s
 					seen[item.Link] = true
 					merged = append(merged, item)
 				}
-				if len(recoveredErrs) > 0 {
+				if len(hardErrs) > 0 {
 					stats.Failed++
-					for _, recoveredErr := range recoveredErrs {
+					for _, recoveredErr := range hardErrs {
 						if len(stats.Errors) < 5 {
 							stats.Errors = append(stats.Errors, recoveredErr)
 						}
@@ -207,6 +208,9 @@ func EvaluateAllCandidatesWithGeminiWithDeadline(service *GeminiService, query s
 				}
 				continue
 			}
+			if len(hardErrs) == 0 {
+				continue
+			}
 			stats.Failed++
 			if len(stats.Errors) < 5 {
 				stats.Errors = append(stats.Errors, batch.err.Error())
@@ -329,6 +333,35 @@ func MergeUniqueRecommendations(base, extra []AIRecommendation) []AIRecommendati
 	return merged
 }
 
+func filterHardGeminiErrors(errs []string) []string {
+	filtered := make([]string, 0, len(errs))
+	for _, item := range errs {
+		if isIgnorableGeminiError(item) {
+			continue
+		}
+		filtered = append(filtered, item)
+	}
+	return filtered
+}
+
+func isIgnorableGeminiError(message string) bool {
+	lower := strings.ToLower(strings.TrimSpace(message))
+	if lower == "" {
+		return false
+	}
+	for _, token := range []string{
+		"no candidate thumbnails or preview frames could be fetched for gemini vision",
+		"candidate thumbnail is low value",
+		"candidate has no thumbnail or preview video",
+		"image url is empty",
+	} {
+		if strings.Contains(lower, token) {
+			return true
+		}
+	}
+	return false
+}
+
 func MergeGeminiBatchStats(base, extra GeminiBatchStats) GeminiBatchStats {
 	merged := base
 	merged.CandidateCap += extra.CandidateCap